Methods for fracturing high temperature well formations

ABSTRACT

This invention provides a fracturing fluid having a high viscosity at temperatures above 200*F comprising an aqueous fluid having a pH of less than 7, a water soluble alcohol and a corsslinked polysaccharide.

.L O O 5 U 125 o D H fl=-30-73 GR 397689566 0 United States Patent 11 1[111 3,768,566

Ely et a1. Oct. 30, 1973 [5 METHODS FOR FRACTURING HIGH 3,096,284 7/1963Slate 155/283 x TEMPERATURE WELL FORMATIONS 3,153,450 10/1964 Foster eta1 166/283 3,167,510 1/1965 Alter 252/855 R Inventors: J W- y; JltenChalterjl; Marlin 3,281,354 10 1966 Scott et a1... 166/283 1). Holtmyer;John M Tinsley, all Of 3,405,062 10/1968 Kuhn 252/855 R Duncan, Okla.3,417,820 12/1968 Epler et a1. 166/308 3,475,334 10/1969 Boudreaux252/855 R 1 1 Asslgneel Halllburton p y Duncan 3,634,237 1 1972 Crenshawet a1.. 252 855 R Okla- 3,696,035 10/1972 Nimerick 166/308 X [22] Filed:Apr. 18, 1972 [21] Appl. No.: 245,278 Primary ExaminerStephen J NovosadRelated U.S. A li ation D t Attorney-John H. Tregoning et a1.

[63] Continuation-impart of Ser. No. 90,301, Nov. 17,

1970, abandoned.

[52] U.S. C1. 166/308, 166/283 [57] ABSTRACT [51] Int. Cl E21b 43/26[58] Field of Search 166/308, 283, 281,

1 2 0; 252/855 R; 10 20 209; Thls mventron provldes a fracturmg fluldhaving a 260/174 ST, 174 R 29.6 MB high viscosity at temperatures above200F comprising an aqueous fluid havin a pH of less than 7, a water {56]References Cited soluble alcohol and a 1:0 slinked polysaccharide.

UNITED STATES PATENTS 2,950,247 8/1960 McGuire, Jr. et a1. 166/280 X 18Claims, N0 Drawings METHODS FOR FRACTURING HIGH TEMPERATURE WELLFORMATIONS This is a continuation-in-part of application Ser. No. 90,301filed Nov. 17, l970, now abandoned.

Hydraulic fracturing is a widely used method for stimulating petroleumproducing subterranean formations and is commonly performed bycontacting a subterranean formation with a viscous fracturing fluidhaving particulated solids, hereinafter referred to as propping agents,suspended therein, applying sufficient pressure to the fracturing fluidto open a fracture in the subterranean formation and maintaining thispressure while injecting the fracturing fluid into the fracture at asufficient rate to extend the fracture into the subterranean formation.When the pressure on the fracturing fluid is reduced, the propping agentprevents the complete closure of the fracture.

Viscous liquids are desirably used as fracturing fluids because theyhave been found to remain in the fracture long enough to permit buildupand maintenance of sufficient pressure to open a fracture. Additionally,a viscous fracturing fluid can support propping agents suspendedtherein.

In order to fracture subterranean formations with temperatures as highas 200, 300, 400F or higher, the fracturing fluid should desirably haveas high a viscosity as a fracturing fluid used for fracturing formationswith lower temperatures. However, viscous fracturing fluids preparedfrom hydratable polysaccharides and hydratable polyacrylamides lose alarge portion of their viscosity on heating to 200F and a majority oftheir viscosity of heating to 400F.

A viscous fracturing fluid for fracturing a 300 or 400F subterraneanformation would necessitate preparing a very viscous fracturing fluid atthe surface in order to have viscosity when the fracturing fluidcontacts the formation. This approach to designing viscous fracturingfluids is limited by the resistance to flow of a highly viscousfracturing fluid through the surface handling equipment and the pipingin the upper portion of the bore hole.

The present invention provides a method whereby the viscosity of a fluidis increased at a time when the fluid is being subjected to temperatureswhich tend to reduce the initial viscosity of the fluid. The viscosityis increased by the hydration of an additive which is a polysaccharidethat has been crosslinked such that the polysaccharides hydration rateis greatly retarded at temperatures below about 100F. However, the bondsbetween the crosslinking agent and polysaccharide are temperaturesensitive and break at temperatures above about 140F, thereby enablingthe aqueous fluid to hydrate the polysaccharide.

More specifically, the viscosity increasing additive, hereinafterreferred to as the retarded gelling agent, of this invention is ahydratable polysaccharide crosslinked with a compound selected from thegroup consisting of dialdehydes having the general formula OHC (CH )nCHO,

wherein n is an integer within the range of to about 3; 2-hydroxyadipaldehyde; dimethylol urea; water soluble urea formaldehyderesins; water soluble melamine formaldehyde resins; and mixturesthereof.

The preferred crosslinking agents for forming the retarded gelling agentof this invention are dialdehydes having the general formula OHC (CH )nCH0 wherein n is an integer within the range of l to about 3. Examplesof dialdehydes within the above general formula are glyoxal,malonicdialdehyde, succinic dialdehyde and glutardialdehyde.

The polysaccharides useful for forming the retarded gelling agent ofthis invention are hydratable polysaccharides having a molecular weightof at least about 100,000 and preferably within the range of about200,000 to about 3,000,000. Suitable hydratable polysaccharides arehydratable galactomannan gums, hydratable glucomannan gums andhydratable cellulose derivatives. Examples of suitable hydratablepolysaccharides are guar gum, locust bean gum, karaya gum,carboxymethylcellulose, carboxymethylhydroxyethylcellulose andhydroxyethylcellulose.

The preferred gelling agent is hydroxyethylcellulose having an ethyleneoxide substitution within the range of about l to about 10 moles ofethylene oxide per anhydroglucose unit. The most preferred gelling agentis hydroxyethylcellulose having an ethylene oxide substitution withinthe range of about 1.3 to about 3 moles of ethylene oxide peranhydroglucose unit.

The concentration of crosslinking agent utilized in the production ofthe retarded gelling agent, the pH of the aqueous fluid and temperaturedetermines the speed at which the bonds between the crosslinking agentand hydratable polysaccharide will be broken to thereby enable theaqueous fluid to hydrate the hydratable polysaccharide. I

The concentration of crosslinking agent necessary to render thehydratable polysaccharides of this invention insoluble in an aqueousfluid having a pH of less than about 7 and a temperature of less thanabout F is within the range of about 0.05 to about 100 parts by weightcrosslinking agent and preferably within the range of about 0.1 to about2 parts by weight crosslinking agent per 100 parts by weightpolysaccharide. Crosslinking agent concentrations of less than about0.05 parts by weight crosslinking agent per 100 parts by weightpolysaccharide do not provide sufficient crosslinking to prevent thepolysaccharide from hydrating within a short time after being contactedwith an aqueous fluid. Crosslinking agent concentrations of greater thanabout 100 parts by weight crosslinking agent per 100 parts by weightpolysaccharide form crosslinked compounds which are too slow to hydrateto be useful in the present inventiorr." j

The hydration rate of the retarded gelling agent is controlled byadjusting the pH of the aqueous, fluid. The retarded gelling agent ofthis invention does not hydrate for extended periods in aqueous fluidhaving a pH of less than about 7 and preferably within the range ofabout 3 to about 4. However, as the temperature of the aqueous fluidapproaches about F the crosslinking bonds are rapidly broken and thegelling agent becomes hydratable.

The retarded gelling agent of this invention is useful for increasingthe viscosity of any aqueous fracturing fluid. However, a fracturingfluid designed to utilize the retarded gelling properties of theretarded gelling agent of this invention has a pH of less than 7, andcontains a gelling agent, water soluble alcohol and an encapsulatedbase.

The pH can be adjusted with any water soluble acid; however, acids suchas fumaric acid and sodium dihydrogen phosphate are preferred because oftheir buffering qualities.

The pH of the aqueous fluid is also a factor as the fracturing fluid isheated to temperatures above about 300F. At temperatures above 300F theacid in combination with the high temperature rapidly degrades thegelling agent and reduces the viscosity of the fracturing fluid.However, by releasing a base into the fracturing fluid at about 300F thedegrading effect of acid can be eliminated.

The base must be one which can be added to the fracturing fluid at thetime of mixing and which will allow the pH of the aqueous fluid toremain below pH 7 until the retarded gelling agent has combined with theaqueous fluid to increase the viscosity thereof. However, as soon as theelevated temperature has broken the polysaccharide-crosslinking agentbond, the pH may be altered. A suitable base, therefore, is one whichhas been encapsulated in a material which will release the base into thefracturing fluid at temperatures above about 150F. Suitable bases areany water soluble chemicals having a pH greater than pH 7. Suitableencapsulating materials are waxes which melt at temperatures above about150F, hydratable methylcellulose and mixtures thereof.

The gelling agents useful in the present invention are hydratablepolysaccharides as previously described and hydratable polyacrylamideshaving a molecular weight of at least about 30,000. Molecular weightsbelow about 30,000 for polyacrylamides and 100,000 for polysaccharideswill generally increase the viscosity of an aqueous fluid, but thehigher molecular weights are more efficient on a per pound basis and arepreferred.

It has been found that when the hydrated gelling agents of thisinvention are mixed with an aqueous fluid containing a small amount ofwater soluble alcohol, the fracturing fluid can better withstand theviscosity reducing effect of temperature. Suitable alcohols arerepresented by the general formula wherein n is an integer within therange of 1 to about and preferably within the range of 1 to about 4.

Examples of alcohols within this formula are methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol,tert-butanol, n-pentanol, 2- methyl- 1 -butanol, 3-methyl- 1 -butanol,2-methyl-2- butanol, 3-methyl-2-butanol, l-methyl-l-butanol andl-ethyl-l-propanol.

The most preferred alcohols are represented by the following generalformula wherein n is an integer within the range of 1 to about 3.

Examples of the most preferred alcohols as represented by this formulaare methanol, ethanol, npropanol and isopropanol.

in a preferred aspect, a fracturing fluid containing the retardedgelling agent of this invention is comprised of water having a pH ofless than 7 and the retarded gelling agent of this invention. The pH ispreferably adjusted by homogeneously mixing within the concentrationrange of 3 to about 20 pounds of a weak acid, such as sodium dihydrogenphosphate, per 1,000 gallons of water. The fracturing fluid preferablycontains within the range of about 10 to about 300 pounds of theretarded gelling agent per 1,000 gallons of water.

In addition to the retarded gelling agent, the fracturing fluidpreferably contains within the range of 10 to 300 and preferably withinthe range of 20 to 100 pounds of the gelling agent, as previouslydescribed, per 1,000 gallons of water.

Fracturing fluids for use at temperatures above about 200F preferablycontain a water soluble alcohol, as previously described, within theconcentration range of about 1 to about 10 and preferably within therange of about 2 to about 7 parts by volume alcohol per 100 parts byvolume of the water.

Fracturing fluids for use at temperatures above about 300F preferablycontain a base, such as sodium bicarbonate coated with a paraffin havinga melting point within the range of about 150F to about 300F, within theconcentration range of about 5 to about 50 pounds of base per 1,000gallons of water.

A fracturing fluid of this invention can also contain fluid loss controladditives, surfactants, propping agents, clay control chemicals, andconcentrations of salt which are compatible with the gelling agent.

The examples are given primarily for the purpose of illustration; andthe invention, in its broader aspects, is not to be construed as limitedthereto.

DATA

Unless otherwise indicated, hydroxyethylcellulose will refer tohydroxyethylcellulose having an ethylene oxide substitution of about 1.5moles of ethylene oxide per anhydroglucose unit.

Crosslinked hydroxyethylcellulose refers to hydroxyethylcellulose havingan ethylene oxide substitution of about 1.5 moles of ethylene oxide peranhydroglucose unit and being crosslinked with about 0.8 parts by weightglyoxal per 100 parts by weight hydroxyethylcellulose.

EXAMPLE I The effect of temperature on the viscosity of a fracturingfluid containing a combination of crosslinked hydroxyethylcellulose andhydroxyethylcellulose is compared to the viscosity of a fracturing fluidcontaining crosslinked hydroxyethylcellulose and a fracturing fluidcontaining hydroxyethylcellulose by first homogeneously mixing theindicated components with water and heating the resulting fluid from to500F in a Fann Model 50 viscometer while taking the 300 RPM dialreading, using a No. 1 spring and sleeve, at the temperature indicatedon Table 1. This reading is reported on Table I as the apparentviscosity of the fracturing fluid in centipoise (cp). Samples A, B and Ccontain 5 parts by volume methanol per parts by volume of water, 10pounds of sodium bicarbonate coated with paraffin per 1,000 gallons ofwater and 10 pounds of sodium dihydrogen phosphate per 1,000 gallons ofwater.

Additionally, Sample A contains 60 pounds of hydroxyethylcellulose and60 pounds of crosslinked hydroxyethylcellulose per 1,000 gallons ofwater, Sample B contains 60 pounds of hydroxyethylcellulose per 1,000gallons of water and Sample C contains 60 pounds of crosslinkedhydroxyethylcellulose per 1,000 gallons of water.

TABLE I Viscosity (cp) Sample 100F 150F 200F 250F 300T 350F 400F 450F500F A 90 230 170 130 80 35 12 3 0 B 75 38 20 5 3 1 O 0 C 2 2 2 28 22 53 0 0 This series of tests illustrate the viscosity characteristics ofthe retarded gelling agent of this invention.

EXAMPLE II The effect of temperature on the viscosity of fracturingfluids containing various crosslinked polysaccharides is determined byfirst homogeneously mixing the indicated components with water, andheating the resulting fluid from 80 to 500F in a Fann Model 50Viscometer while taking the 300 RPM dial reading, using a No. 1 springand sleeve, at the temperature indicated on Table II. This reading isreported on Table II as the apparent viscosity of the fracturing fluidin centipoise (cp).

Samples A through D contain 60 pounds of hydroxyethylcellulose per 1,000gallons of water, 5 parts by volume methanol per 100 parts by weight ofwater and sufficient sodium dihydrogen phosphate to adjust the pH of thewater to about 5.5.

Additionally, Sample A contains 60 pounds of hydroxyethylcellulose per1,000 gallons of water, Sample B contains 60 pounds per 1,000 gallons ofwater of hydroxyethylcellulose crosslinked with about l0v parts byweight glutardialdehyde per 100 parts by weight hydroxyethylcellulose,Sample C contains 60 pounds per 1,000 gallons of water of guar gumcrosslinked with about 20 parts by weight glyoxal per 100 parts byweight hydroxyethylcellulose, and Sample D contains 60 pounds per 1,000gallons of water of hydroxyethylcellulose crosslinked with about 0.8parts by weight glyoxal per 100 parts by weight hydroxyethylcellulose.

This series of tests illustrate the low initial viscosity of afracturing fluid containing a crosslinked polysaccharide as compared tothe high initial viscosity of an unretarded polysaccharide. This seriesalso illustrates the temperature stability of a variety of crosslinkedpolysaccharides.

EXAMPLE I The temperature stability of various gelling agents arecompared by first homogeneously mixing the indicated components withwater, heating the resulting fluid to 250F in a Fann Model 50 viscometerand maintaining the fluid at 250F for the time indicated on Tables IIIand IV before taking the 300 RPM dial reading, using a No. 1 spring andsleeve. This reading is reported on Tables III and IV as the apparentviscosity of the fluid in centipoise (cp).

Sample A contains 90 pounds per 1,000 gallons of water ofhydroxyethylcellulose having an ethylene oxide substitution of about 1.5moles of ethylene oxide per anhydroglucose unit and 1 part by weightpotassium chloride per 100 parts by weight of water.

Sample B contains 90 pounds per 1,000 gallons of water ofhydroxyethylcellulose having an ethylene oxide substitution of about 1.8moles of ethylene oxide per anhydroglucose unit and 1 part by weightpotassium chloride per 100 parts by weight water.

Sample C contains 90 pounds per 1,000 gallons of hydroxyethylcellulosehaving an ethylene oxide substitution of about 2.5 moles of ethyleneoxide per anhydroglucose unit and 1 part by weight potassium chlorideper 100 parts by weight of water.

Sample D contains 90 pounds per 1,000 gallons ofcarboxymethylhydroxyethylcellulose having an ethylene oxide substitutionof about 1.5 moles of ethylene oxide per anhydroglucose unit and acarboxymethyl substitution of about 0.2 moles of carboxymethyl anhydroglucose unit and 1 part by weight potassium chloride per 100 parts byweight water.

Sample E contains pounds per 1,000 gallons of a copolymer of acrylamideand vinyl chloride and 1 part by weight potassium chloride per parts byweight water.

Samples A and E correspond to Samples A through E except that Samples Aand E additionally contain 5 parts by volume methanol per 100 parts byvolume of water.

TABLE 111 Viscosity (cp) Sample 0 hr. V2 hr. 1 hr. 1% hr. 2 hrs. 2 hrs.3 hrs.

A 54 29 22 18 16 13 1 1 B 30 22 18 15- 13 7 ll 10 C 55 33 18 I0 7 3 1 D12.5 13 10 8 7.5 7 6 E 32.5 23 21 19 18 l7 l6 TAB LE IV Viscosity (cp)Sam ple 0 hr. 92 hr. 1 hr. 1% hr. 2 hrs. 2% hrs. 3 hrs.

A 65 60 53 48 44 41 36 B 46 40 37 34 33 33 32.5 C 51 41 34 31 27.5 25 23D 14 24 28 25 22 18 16 E 37.5 34 32.5 32.5 32 32 31 Tables III and IVillustrate the temperature stability of various polysaccharides and theeffect of alcohol on reducing the thermal degradation ofpolysaccharides.

EXAMPLE IV The comparative ability of two weak acids to control thehydration rate of crosslinked hydroxyethylcellulose is determined byfirst homogeneously mixing the indicated components with water, heatingthe resulting fluid to 140F in a Fann Model 50 Viscometer andmaintaining the fluid at 140F for the time indicated on Table V beforetaking the 300 RPM dial reading, using a No. 1 spring and sleeve. Thisreading is reported on Table V as the apparent viscosity in centipoise(cp).

Sample A contains 30 pounds of hydroxyethylcellulose, 60 pounds ofcrosslinked hydroxyethylcellulose, 20 pounds of sodium dihydrogenphosphate and 20 pounds of paraffin coated borax per 1,000 gallons ofwater.

Sample B contains 30 pounds of hydroxyethylcellulose, 60 pounds ofcrosslinked hydroxyethylcellulose, 15 pounds of a blend of 70 parts byweight fumaric acid 30 parts by weight sodium carbonate per 100 parts byweight of the blend, and 25 pounds of paraffin coated borax per 1,000gallons of water.

B l l6 19 20 27 38 75133153161 This data indicates that a blend offumaric acid and sodium carbonate is more efficient than sodiumdihydrogen phosphate at delaying the hydration time of crosslinkedhydroxyethylcellulose.

EXAMPLE V The temperature stability of three viscous fracturing fluidsare determined by first homogeneously mixing the indicated componentswith water, heating the resulting fluid to 250F in a Fann Model 50Viscometer and maintaining the fluid at 250F for the time indicated onTable V1 before taking the 300 RPM dial reading, using a No. l springand sleeve. This reading is reported on Table VI as the apparentviscosity of the fracturing fluid in centipoise (cp).

Sample A contains 120 pounds hydroxyethylcellulose per 1,000 gallons ofwater, 1 part by weight potassium chloride per 100 parts by weightwater, and parts by volume isopropylalcohol per 100 parts by volumewater.

Sample B contains 100 pounds hydroxyethylcellulose per 1,000 gallons ofwater, 1 part by weight potassium chloride per 100 parts by weightwater, and 5 parts by volume isopropyl alcohol per 100 parts by volumewater.

Sample C contains 120 pounds hydroxyethylcellulose per 1,000 gallons ofwater and 1 part by weight potassium chloride per 100 parts by weightwater.

TABLE VI Viscosity (cp) Sample 0.5 hr. 1.5 hrs. 2.0hrs. 3.0hrs. 4.0hrs.5.0hrs. 6.0hrs.

A 111.5 107.5 104.5 100 97.5 94.5 93.5 B 75 71.5 68.5 64 62 61 61 C 8871.5 60 46.5 37.5 31 26.5

it is not intended to be limited except as indicated in the appendedclaims.

What is claimed is: l. A method of fracturing a subterranean formationcomprising:

contacting said formation with an aqueous fluid comprising a hydratablepolysaccharide cross-linked with a compound selected from the groupconsisting of dialdehydes having the general formula:

OHC (Cl-1 CHO wherein n is an integer within the range of 0 to about 3,2-

hydroxyadipaldehyde, dimethylol urea, water soluble urea formaldehyderesins, water soluble melamine formaldehyde resins and mixtures thereof,wherein said fluid has a pH of less than applying sufficient pressure tosaid fluid to fracture said formation; and maintaining said pressurewhile forcing said fluid into said fracture. 2. The method of claim 1wherein said fluid is further comprised of an alcohol having the generalformula:

wherein Y n is an integer within the range of 1 to about 5 and mixturesthereof.

3. The method of claim'2 wherein said fluid is further comprised of abase coated with a material which is insoluble in said fluid and has amelting point within the range of about F to about 300F.

4. The method of claim 3 wherein said fluid is further comprised of agelling agent selected from the group consisting of a hydratablepolysaccharide having a molecular weight of at least about 100,000; ahydratable polyacrylamide having a molecular weight of at least about30,000 and mixtures thereof.

5. The method of claim 4 wherein said gelling agent ishydroxyethylcellulose having an ethylene oxide substitution within therange of about 1.3 to about 3 moles of ethylene oxide per anhydroglucoseunit.

6. The method of claim 3 wherein said base is coated with wax having amelting point within the range of about 150F to about 300F.

7. The method of claim 2 wherein said alcohol has the general formula: Y

wherein n is an integer within the range of 1 to about 4.

8. The method of claim 2 wherein said alcohol has the general formula:

wherein 'n is an integer within the range of 1 to about 3.

9. The method of claim 1 wherein said polysaccharide is selected fromthe group consisting of galactomannan gums, glucomannan gums, cellulosederivatives and mixtures thereof, said polysaccharide having a molecularweight of at least about 100,000.

10. The method of claim 9 wherein said cellulose derivative ishydroxyethylcellulose having an ethylene oxide substitution within therange of about 1 to about 10 moles of ethylene oxide per anhydroglucoseunit.

11. The method of claim 10 wherein said ethylene oxide substitution iswithin the range of about 1.3 to about 3 moles of ethylene oxide peranhydroglucose unit.

12. The method of claim 1 wherein said polysaccharide is crosslinkedwith a dialdehyde selected from the group consisting of dialdehydeshaving the general formula:

OHC (CH CHO,

wherein n is an integer within the range of to about 3.

13. The method of claim 1 wherein said polysaccharide is crosslinkedwith glyoxal.

14. The method of claim 1 wherein said polysaccharide is crosslinkedwith glutardialdehyde.

15. The method of claim 1 wherein said pH is within the range of about 3to about 4.

16. The method of claim 1 wherein said polysaccharide is crosslinkedwith said compound at a concentration within the range of about 0.05 toabout 100 parts by weight of said compound per 100 parts by weight ofsaid polysaccharide.

17. A method of fracturing a subterranean formation comprising:

contacting said formation with an aqueous fluid comprisinghydroxyethylcellulose having an ethylene oxide substitution within therange of about 1.3 to

about 3 moles of ethylene oxide per anhydroglucose unit and beingcrosslinked with glyoxal at a concentration within the range of about0.1 to about 2 parts by weight glyoxal per parts by weight of saidhydroxyethylcellulose, within the range of 2 to about 7 parts by volumeper 100 parts by volume of said aqueous fluid of an alcohol having thegeneral formula:

wherein n is an integer within the range of l to about 3, and within therange of about 5 to about 50 pounds per 1000 gallons of said aqueousfluid of a base coated with wax having a melting point within the rangeof about F to about 300F, wherein said fluid has a pH of less than 7;applying sufficient pressure to said fluid to fracture said formation;and maintaining said pressure while forcing said fluid into saidfracture.

18. The method of claim 17 wherein said fluid further comprises withinthe range of about 10 to about 300 pounds per 1,000 gallons of saidaqueous fluid of hydroxyethylcellulose having an ethylene oxidesubstitution within the range of about 1.3 to about 3 moles of ethyleneoxide per anhydroglucose unit.

, NITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No.3,768,566 Dated Oct. 30, 1973 John W. Ely; Jiten Chatterji; Inventor(s)Marlin D. Holtmyer; John M. Tinsley It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 32, delete the word "of" and insert therefor -on-. Column6, lines 9-10, delete the phrase "per 1,000 gallons of water."

Line 12, after the word "unit" insert per 1,000

gallons of water--.

Lines 14-15, delete the phrase "per 1,000 gallons of water."

Line 17, after the word "unit" insert per 1,000

gallons of water-.

Line 19, delete the phrase "per 1,000 gallons." Line 22, after the word"unit" insert -per 1,000

gallons of water a, 7

Line 2 1-, delete the phrase "per 1,000 gallons. Line 29, after the word"unit" insert -per 1,000

gallons of water--.

Line 31, delete the phrase "perv 1,000 gallons." Line 32, after the word"chloride" insert -per 1,000

gallons of water- Column 7, line 32, delete the word "are" andsubstitute therefor In the Abstract, last line, correct "corsslinked" toread --crosslinked-.

Signed and sealed this 9th day of April 19714..

(SEAL) Attest:

EDWARD NLFLLTCHERJR. 0. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-IOSO (10-69) USCOMMC: 637MP69 U.S. GOVERNMENT PRINTINGOFFICE: I), 0-366-334.

2. The method of claim 1 wherein said fluid is further comprised of analcohol having the general formula: CnH(2n 1)OH, wherein n is an integerwithin the range of 1 to about 5 and mixtures thereof.
 3. The method ofclaim 2 wherein said fluid is further comprised of a base coated with amaterial which is insoluble in said fluid and has a melting point withinthe range of about 150*F to about 300*F.
 4. The method of claim 3wherein said fluid is further comprised of a gelling agent selected fromthe group consisting of a hydratable polysaccharide having a molecularweight of at least about 100,000; a hydratable polyacrylamide having amolecular weight of at least about 30,000 and mixtures thereof.
 5. Themethod of claim 4 wherein said gelling agent is hydroxyethylcellulosehaving an ethylene oxide substiTution within the range of about 1.3 toabout 3 moles of ethylene oxide per anhydroglucose unit.
 6. The methodof claim 3 wherein said base is coated with wax having a melting pointwithin the range of about 150*F to about 300*F.
 7. The method of claim 2wherein said alcohol has the general formula: CnH(2n 1)OH, wherein n isan integer within the range of 1 to about
 4. 8. The method of claim 2wherein said alcohol has the general formula: CnH(2n 1)OH, wherein n isan integer within the range of 1 to about
 3. 9. The method of claim 1wherein said polysaccharide is selected from the group consisting ofgalactomannan gums, glucomannan gums, cellulose derivatives and mixturesthereof, said polysaccharide having a molecular weight of at least about100,
 000. 10. The method of claim 9 wherein said cellulose derivative ishydroxyethylcellulose having an ethylene oxide substitution within therange of about 1 to about 10 moles of ethylene oxide per anhydroglucoseunit.
 11. The method of claim 10 wherein said ethylene oxidesubstitution is within the range of about 1.3 to about 3 moles ofethylene oxide per anhydroglucose unit.
 12. The method of claim 1wherein said polysaccharide is crosslinked with a dialdehyde selectedfrom the group consisting of dialdehydes having the general formula: OHC(CH2)n CHO, wherein n is an integer within the range of 0 to about 3.13. The method of claim 1 wherein said polysaccharide is crosslinkedwith glyoxal.
 14. The method of claim 1 wherein said polysaccharide iscrosslinked with glutardialdehyde.
 15. The method of claim 1 whereinsaid pH is within the range of about 3 to about
 4. 16. The method ofclaim 1 wherein said polysaccharide is crosslinked with said compound ata concentration within the range of about 0.05 to about 100 parts byweight of said compound per 100 parts by weight of said polysaccharide.17. A method of fracturing a subterranean formation comprising:contacting said formation with an aqueous fluid comprisinghydroxyethylcellulose having an ethylene oxide substitution within therange of about 1.3 to about 3 moles of ethylene oxide per anhydroglucoseunit and being crosslinked with glyoxal at a concentration within therange of about 0.1 to about 2 parts by weight glyoxal per 100 parts byweight of said hydroxyethylcellulose, within the range of 2 to about 7parts by volume per 100 parts by volume of said aqueous fluid of analcohol having the general formula: CnH(2n 1)OH wherein n is an integerwithin the range of 1 to about 3, and within the range of about 5 toabout 50 pounds per 1000 gallons of said aqueous fluid of a base coatedwith wax having a melting point within the range of about 150*F to about300*F, wherein said fluid has a pH of less than 7; applying sufficientpressure to said fluid to fracture said formation; and maintaining saidpressure while forcing said fluid into said fracture.
 18. The method ofclaim 17 wherein said fluid further comprises within the range of about10 to about 300 pounds per 1,000 gallons of said aqueous fluid ofhydroxyethylcellulose having an ethylene oxide substitution within therange of about 1.3 to about 3 moles of ethylene oxide per anhydroglucoseunit.